What causes some trees to have purple leaves?

Question

What causes some trees to have purple leaves?

Answer 1

One way a plant uses pigments is in chromoplasts (similar to chloroplasts, where chlorophyll is found, but not photosynthetic). Chromoplasts protect the tree from oxidation. These will be found in plants with red or copper leaf colors. A Copper Beech tree has anthocyanin, a pigment that reflects red and acts as an antioxidant. Thus the leaves of the copper beech have more red chromoplasts that overwhelms the chloroplast’s green. The leaves appear deep red in sunlight however when you look at a copper beech in the shade that copper coloration thins out, and you can see the green photosynthetic chlorophyll showing through because the tree is still actively photosynthesizing. Plants with more chromoplasts can survive habitats with marginal resources where they are better protected from both oxidative and UV stress.

Chromoplast content varies naturally in plant leaves. Plants with more chromoplasts can survive regions of marginal resources where they are better protected from both oxidative and UV stress. Photosynthesis results in plants with the highest internal oxygen concentrations of any organism. Plants under oxidative stress switch on pigment manufacturing genes in the chromoplast to have more antioxidants. Another important function of pigments is as an internal sun screen and/or light trap to stop UV from damaging the plant.

The green leaved sugar maple is more sensitive to nutrient stresses associated with low pH soils than the red maple (Acer rubrum). An increase in chromoplast content can offset the negative effects of nutrient imbalances on maples by relieving UV & oxidative stress. Red maples can out compete other maples in nutrient poor, acidic soils by having more chromoplasts. http://www.ingentaconnect.com/content/bs...

Chlorophyll a is unstable and must continually be replaced. Light is only one essential for chlorophyll manufacture. Marginal quantities of Mg, Fe, or nitrogen strongly limit the rate that chlorophyll can be manufactured. Weathered acid soil is a poor habitat for nitrifying (nitrogen fixing) bacteria that are sensitive to low pH, so less nitrogen is available to the plants.  Fe becomes soluble as pH increases so is washed away. Then Mg is leached out of the soil as pH drops. This reduces the rate of chlorophyll production so the plant grows slower. More chromoplasts relieve the plant of some stress and protect it from UV allowing it to use marginal habitat.

http://www.rsc.org/delivery/_ArticleLink...

Answer 2

if i remember correctly (some time since i last studied botany :) they have a different pigment which absorbs life like chlorophyll just absorbs different colors of light